Fireproof filtering material



April 20, 1937. F; J. HOOKER ET AL 2,078,197

FIREPROOF FILTERING MATERIAL Filed Jan. 15, 1935 BY W Mm WwdfI/rvd ATTORNEYS Patented Apr. 20, 1937 UNITED STATES; PATENT orrics ma.m mfififfsfiffis a.

Carruthcrs, Glendale, Ohio, assignors to The Stearns 8; Foster Company, Lockland, Ohio, a

corporation of Ohio Application 1m 15,1935, ,No. 1,934

"' .SCIaims. (cuss-2.5)

This invention relates to a fire-proof filtering material adapted particularly to filter air in.

air conditioning [The invention likewise relates toa preferred method of 5 this material.

Many types of filterhave been 'used in air conditioning systems with varyin degrees of success. It is desirable that the filtering material employedbe relatively inexpensive so that it may be replaced from time to time, that it be easy to, handle so that'less expert workmanship is required either for installation or replacement; and that its consistency be such that it removes even the finest dirt or soot particles from the atmosphere without impeding too greatly the air fiow. Inasmuchas the filter in an air conditioning system is usually connected with a plurality of rooms by conduits,: and inasmuch as a forced draft is maintained through the conduit system, it is highly desirable that the filtering material be fire proof *or at least suiiiciently so not to actively blaze.

The object of this invention is to provide a" filtering material possessing the properties 'pre viously specified as desirable in a material of thistype.

Another object oi the invention is to provide a method or process of constituting such ma-" physical stability to withstand passage of the current of air, together with a permeability which is neither too great nor too small. The as required permeability tendsto be inconsistentwith the required physical stability. The problem is to proportion these two properties in constituting the filtering membrane so that it may be employed. successfully in commercial air con- 50 ditioning systems of the type at present in use.

The filtering material of this invention comprises a sheet of carded cotton fibers, the outer surface fibers on each side of thesheet being adhesively united suficiently to give the sheet so a structural stability, but the adhesive or sizing constituting used to unite the outer surface fibers. being applied so that the porosity and permeability of the sheet is not materially diminished with respect to the passage of air current.

Referring to the drawing, the membrane is 5'- generally indicated by I. 'Figure 2 shows a skin 2-! alp' 'plied on either side oi a loosely knit,-carded fiber cover 3 of relatively greater porosity, but having high. dirt collective qualities. In Figure 3 the skin 2 is applied to only one side 10 of the carded fiber sheet 3. g a The cotton fibers are impregnated with a material adapted to reduce their infiammability. This impregnation of the fibers, in contra distinction to a fiher surface coating, accomplishes 15- the desired fire-proofing objectivefwithout detracting from the felting property of the fibers or their or dust collecting characteristics.

ing material is' used to comprehend materials which materially reduce the tendency oi cotton fiber to burn with afiam.e, and is not intended to designate solely materials which render the fiber indestructible by heat.-* Onesolution s'uitable for fire-proofing the cotton fibers comprises:

4% borax, 4% boric acid,-8% dlammonium acid] phosphate, all dissolved in water. The percentages of the specified ingredients .are all based on the weight of the water of the solution;

The percentages oi the ingredients above are not critical but in general the may; amount oi fire-proofing ingredients inthe solu tion results in greater fire-proofing, for instance, the diammonium acid phosphate disclosed above may vary from 4 to 20%. As examples, the 1501- 40 lowing other types of fire-proofing solutions are disclosed:

Example-1 a Y Percent Ammonium chloride 6 v Calcium chloride .j 6

, Examplez 1 7 Percent Calcium chloride '& Ammonium chloride -l 4 Ammonium sulphate 4 Generally speaking; the preferred ingredients of the fire-proofing solution when incorporated into the fiber have the chemical action of producs5 ing a non-combustible gas when the fibers are subject toheat. It is desired that the ingredients used for fire-proofing have the capacity to produce a comparatively large amount of gas when 5 the impregnated fibers are subjected to a relatively low temperature otherwise sumcient to causeignitionofuntreatedfibers.

Preferably, the cotton fibers are dry when being put in this solution as the dry fibers absorb the solution more readily than fibers which are already of high moisture content. Complete'immersion of the fibers in a solution of this nature for a period of two to ten minutes is sufiicient for impregnation After impregnation and fire-proofing of the fibers, the fibers are then dried and carded into a sheet of requisite thickness. One such sheet susceptible to use asafilteringmembraneis of such thickness that the sheet weighs .8 ounce per square yard. The sheet may, however, be made thinner or thicker, depending upon the type of filtering equipment in which the membrane is to be used, the pressure and velocity of the air to be passed therethrough, and the nature of contaminaticmoftheairbeingfiltered. In general, the method of constituting the sheet from the carded, impregnated, non-1e fibers, is similar to that described as the old or customary method in Loomis Patent No. 1,928,568. The sheet so aftercarding to the requisite weight is compressed tothedesired thickness andistreatedwitha surface sizing adapted to act as an adhesive for lmiting the surface webs into a lace-like or lattice structure.

Though many types of adhesive may be succesfully employed, a dilute sizing solution such as one-half to three percent approximately of animal glue in water, or a dilute starch solution. may be used. This solution may be applied to o the sheet by spraying or brushing or passing the 'sheetthroughrollsin'suchamannerandinsuch quantity that the size or adhesive when applied to the sheet unites the fibers structurally into a discontinuous coating or porous skin but does not obiectionably impair membrane permeability.

This membrane when so constituted is characterized by a core of loosely knit and united cotton fibers anda surface lattice on one or both sides of the core of relatively great structural in stability as compared to the core, but having a porosity or air permeability enabling the sheet to be used as a filter without great increase in pressure loss of air fiowing therethrough. If desired, a membrane may be constituted according 55 to the-foregoing description and split into halves as disclosed in Figure 3, each of the halves being adapted for use as separate filtering membranes. The membrane of our invention may then be folded upon itself or rolled upon itself to facilirtate packing and shipment and at the time of use spread out in membrane form without contiguous layers adhering to each other. In use, this material is possessed of the structural stability to withstand the air current now 'Ihefiberadmtopreservaticnoftheirfelting quality in the fire-proofing treatment. are appropriately related to constitute a strong membrane which is of great dirt collecting capacity without impairment of permeability.

The nonor fire-proof nature of the composition permits the utilimtion-od a product of this type with its attendant advantages. whereas otherwise suehafilteringmaterial might constitute a very objectionable fire hasard.

Having described our-invention, desireto be limited only by the ensuing claim:

1. Inainairfiltenafilteringmembraneadapted for air conditioning, said membrane, comprising, a-thinlayerofcardedcottonfibers withamaterial adaptedto reducetheirinfiammability. said layer surfaced with a discontinuous coating of adhesive adaptedto hold said carded fibers together structurally without materially impairing the permeability of-the layer.

2. In an air conditioning system, a filter membrane, said membrane comprising, cotton fibers impregnated with non-inflammable solids. said fibers cardedinto athinsheet andcoveredoneach side with a discontinuous adhesive coating adapted to impart to the membrane-the structural stability requisite for withstanding the passage ofair without materially d its permeability.

3. A non-hie filtering memhranedn' an air conditioning system comprising, a sheet of carded cotton fibers surfaced with a skin of cotton fibers adhesiveiy united into a lattice struc ture of relatively high air permeability, said card-- ed cotton fiber containing boric acid. horas, and

diammonium acid phosphate.

4. A filtering membrane for use in an air cone ditioning system, said membrane comprising; a

sheet of carded cotton fibers oi requisite thickness coveredon eachsidebyaporousskinof cotton fibers flexibly adhesively united to form a lattice structure w: of structural stability as compared to the carded cotton sheet, said carded cotton fiber homogeneously imm'esnated with inorganic chemicals adapted to evolve a noncombustible gas when said sheet is heated to a temperature co to the ignition temperature of cotton fiber.

5. A non-le filtering membrane foruse in air conditioning systems compridng, a' sheet of carded cotton fibers surfaced with a skin of cotton fibers adhesively united into a lattice mnnmcx J. Boom.

JAMES R. CARRUTHERS. 

